Current delay devices are presently made of RC circuits. Adjusting the delay is done by varying the resistance and/or capacitance. In an integrated circuit with field effect transistors, for instance of the MOS (metal oxide semiconductor) type, the resistance and capacitance are ordinarily constituted by transistors.
The disadvantage of such delay devices is the exponential curve of the variation in the delay with respect to the variation of the value of R and C. The linearity of the adjustment of the delay accordingly requires high-resistance and high-capacitance RC products, and this is incompatible with very short delay times. On the other hand, RC circuits must be inserted between input and output buffer circuits, making the external circuits insensitive to variations in R and C. Moreover, the technology for manufacturing field effect transistors engenders major fluctuations in the characteristics of the transistors of different integrated circuits. These fluctuations are an obstacle to the desired reliability and fineness of the delay adjustment.